Combinations of caps and vessels are commonly used for receiving and storing specimens. In particular, biological and chemical specimens may be analyzed to determine the existence of a particular biological or chemical agent. Types of biological specimens commonly collected and delivered to clinical laboratories for analysis may include blood, urine, sputum, saliva, pus, mucous, cerebrospinal fluid and others. Since these specimen-types may contain pathogenic organisms or other harmful compositions, it is important to ensure that vessels are substantially leak-proof during use and transport. Substantially leak-proof vessels are particularly critical in cases where a clinical laboratory and a collection facility are separate.
To prevent leakage from the vessels, caps are typically screwed, snapped or otherwise frictionally fitted onto the vessel, forming an essentially leak-proof seal between the cap and the vessel. In addition to preventing leakage of the specimen, a substantially leak-proof seal formed between the cap and the vessel may reduce exposure of the specimen to potentially contaminating influences from the surrounding environment. A leak-proof seal can prevent introduction of contaminants that could alter the qualitative or quantitative results of an assay as well as preventing loss of material that may be important in the analysis.
While a substantially leak-proof seal may prevent specimen seepage during transport, physical removal of the cap from the vessel prior to specimen analysis presents another opportunity for contamination. When removing the cap, any material that may have collected on the under-side of the cap during transport may come into contact with a user or equipment, possibly exposing the user to harmful pathogens present in the sample. If a film or bubbles form around the mouth of the vessel during transport, the film or bubbles may burst when the cap is removed from the vessel, thereby disseminating specimen into the environment. It is also possible that specimen residue from one vessel, which may have transferred to the gloved hand of a user, will come into contact with specimen from another vessel through routine or careless removal of the caps. Another risk is the potential for creating a contaminating aerosol when the cap and the vessel are physically separated from one another, possibly leading to false positives or exaggerated results in other specimens being simultaneously or subsequently assayed in the same general work area through cross-contamination.
Concerns with cross-contamination are especially acute when the assay being performed involves nucleic acid detection and an amplification procedure, such as the well known polymerase chain reaction (PCR) or a transcription based amplification system (TAS), such as transcription-mediated amplification (TMA) or strand displacement amplification (SDA). Since amplification is intended to enhance assay sensitivity by increasing the quantity of targeted nucleic acid sequences present in a specimen, transferring even a minute amount of specimen from another container, or target nucleic acid from a positive control sample, to an otherwise negative specimen could result in a false-positive result.
A pierceable cap can relieve the labor of removing screw caps prior to testing, which in the case of a high throughput instruments, may be considerable. A pierceable cap can minimize the potential for creating contaminating specimen aerosols and may limit direct contact between specimens and humans or the environment. Certain caps with only a frangible layer, such as foil, covering the vessel opening may cause contamination by jetting droplets of the contents of the vessel into the surrounding environment when pierced. When a sealed vessel is penetrated by a transfer device, the volume of space occupied by a fluid transfer device will displace an equivalent volume of air from within the collection device. In addition, temperature changes can lead to a sealed collection vessel with a pressure greater than the surrounding air, which is released when the cap is punctured. Such air displacements may release portions of the sample into the surrounding air via an aerosol or bubbles. It would be desirable to have a cap that permits air to be transferred out of the vessel in a manner that reduces or eliminates the creation of potentially harmful or contaminating aerosols or bubbles.
Other existing systems have used absorptive penetrable materials above a frangible layer to contain any possible contamination, but the means for applying and retaining this material adds cost. In other systems, caps may use precut elastomers for a pierceable seal, but these caps may tend to leak. Other designs with valve type seals have been attempted, but the valve type seals may cause problems with dispense accuracy.
Ideally, a cap may be used in both manual and automated applications, and would be suited for use with pipette tips made of a plastic material.
Generally, needs exist for improved apparatus and methods for sealing vessels with caps during transport, insertion of a transfer device, or transfer of samples.